1. Field of the Invention
The invention relates to a process for soldering optical elements to metal mountings and mounting assemblies, and more particularly, to a process for connecting a transparent optical element to metal mounting. The invention also relates to a mounting assembly of transparent optical element and a metal mounting.
2. Discussion of Relevant Prior Art
The brazing of quartz glass and the like to a nickel-iron alloy, with an intermediate ring of aluminum coated with zinc or zinc and gold or silver, is known from German Laid-Open Patent DE 38 27 318 A. The parts are brazed in a furnace at about 600xc2x0 C. The patent focuses on the degree of sealing of the joint.
Japanese Laid-Open Patent JP 1/215745 A (Derwent WPI Abstract) describes oven soldering of quartz glass to metal, with a solder of indium, tin, silicon carbide and carbon at temperatures above 100xc2x0 C. and under pressure. Coatings are not provided. Stresses are diminished by the solder layer. According to Japanese Patent Document JP 58/120578 A (Derwent WPI Abstract), quartz, borosilicate glass or other materials are coated with a film of noble metal, preferably by firing a paste. A metal part is coated with titanium or zirconium and then with silver solder or silver-copper solder. The two parts are brought together and are heated in a vacuum or under protective gas. The hard solder used makes high temperatures necessary. The parts are preferably of complex shapes, and are porous or foam-like. Optical elements are not mentioned.
The object of the invention is to provide a technique by which optical elements can be soldered to mountings. For this purpose, low process temperatures which lie below 200xc2x0 C. and eventually even below 150xc2x0 C. must be maintained to protect thin optical layers, as well as the lens material itself, for example, optical glass, quartz glass, calcium fluoride, or other fluorides. Likewise, thermal and other stresses, including compressive stresses during, before and after the soldering process, are to be kept to a minimum since they present a considerable danger to the permanence of the material and to optical functioning. Sufficient strength of the joint must be attained, with a tensile shear strength above about 10 N/mm2.
This object is attained by a process for connection a part of transparent material with a metal part in a connecting region comprising: applying an adhesion layer and a solderable diffusion barrier to the transparent material part in the connecting region, applying a solder layer to the metal part, positioning the transparent material part and the metal part on each other, and bringing the transparent material part and the metal part in common to the melting temperature of the solder layer. The object is also attained through the use of an assembly, at comprising: a part made of transparent material, a metal part soldered thereto, a solder connection having a layer structure comprising: transparent material of the transparent material part, an adhesion layer, a diffusion barrier layer, a first oxidation protection layer, a second oxidation protection layer, a solder layer, and metal of the metal part, with transitions between the layers.
Soldering with a common temperature supply to all parts keeps thermal stresses minimal. This is supported by the use of low-melting solder.
The first coatings of both parts insure good strength; the respective antioxidation layers make possible simple manipulation, with the elimination of fluxes which represent a considerable risk in particular to the optical surfaces of lenses.